IERC1155

A single IERC1155 contract can manage an infinite number of distinct token types, each identified by a unique uint256 token ID. This allows for:

• Fungible tokens: Where balances are tracked in aggregate (e.g., 1000 'Gold Coins' with ID #1).
• Non-fungible tokens (NFTs): Where the balance for a specific ID is 1 (e.g., a unique 'Legendary Sword' with ID #999).
• Semi-fungible tokens: A hybrid model where items can be fungible in quantity but have unique metadata.

The standard is optimized for gas efficiency through native support for batch transfers and balance queries. Key functions include:

• safeBatchTransferFrom: Transfers multiple token types (IDs) and amounts in a single transaction, drastically reducing gas costs versus multiple individual transfers.
• balanceOfBatch: Queries the balances of multiple token IDs for multiple addresses in one call.
• safeBatchTransferFrom is the atomic, recommended method, ensuring all transfers succeed or the entire transaction reverts.

IERC1155 uses a simplified, omnipotent approval system via the setApprovalForAll function. This grants or revokes permission for a specific operator address to manage all of the caller's tokens within that contract. This differs from ERC-20's per-spender allowance and is more akin to ERC-721's model. For granular control, the standard also includes the isApprovedForAll view function to check operator status.

Token metadata is provided via the uri(uint256 id) function, which returns a URI (e.g., an IPFS hash) pointing to a JSON file for a specific token ID. This JSON follows a standardized schema defining the token's name, description, image, and attributes. A single contract can use a base URI with the token ID appended (e.g., https://api.example.com/{id}.json), allowing for efficient, deterministic metadata resolution for all tokens.

The safeTransferFrom and safeBatchTransferFrom functions include a data parameter and implement receiver checks to prevent accidental loss of assets. If the receiving address is a smart contract, these functions call onERC1155Received or onERC1155BatchReceived on that contract. This hook allows the receiver to implement logic to accept or reject the transfer, which is critical for enabling trustless marketplaces, vaults, and other composable DeFi applications.

While the core IERC1155 interface is non-opinionated about minting, common extension interfaces like OpenZeppelin's ERC1155Supply add crucial functionality:

• Total Supply Tracking: The totalSupply(uint256 id) function returns the total circulating amount of a specific token ID.
• Minting & Burning: Functions like _mint and _burn are internal helpers used by contract developers to create (mint) new tokens or destroy (burn) existing ones, updating both individual balances and the total supply.

The standard can represent a non-fungible token (the whole asset) and its fungible tokens (ownership shares) within the same contract. This enables fractional ownership of high-value assets like real estate or art. Mechanism:

• The NFT token ID 1 represents the whole asset.
• Fungible token ID 2 represents 1,000,000 ownership shares.
• The contract enforces the link between the NFT and its fractions.

IERC1155 efficiently handles event ticketing and tiered memberships. A concert contract could issue:

• 5,000 General Admission tickets (fungible, ID: 1).
• 50 VIP Pass tokens (fungible, ID: 2).
• 1 Backstage Pass NFT (non-fungible, ID: 3). Batch minting to organizers and batch transfers to buyers significantly reduce transaction overhead compared to individual ERC-721 mints.

Perfect for trading card platforms or digital art collections where users complete sets. A contract can manage:

• Common cards with a supply of 10,000 each (fungible).
• Rare, serial-numbered holographic cards (non-fungible). The balanceOfBatch function allows a marketplace to verify a user's entire collection in a single call, enabling efficient set completion checks and bundled sales.

Enables the creation of a single vault token representing a basket of underlying assets. A user can deposit multiple ERC-20 tokens and receive a single IERC1155 vault receipt token (fungible). This receipt can then be used as collateral or traded. Advantage: Simplifies portfolio management and collateralization by representing a complex basket with a single token ID, while the contract tracks the underlying assets via the uri metadata.

IERC1155's efficient batch operations make it well-suited for bridging assets between blockchains. A bridge contract can lock multiple token types on one chain and mint their wrapped equivalents on another in a single batch transaction. This is more gas-efficient than bridging each ERC-721 or ERC-20 asset individually. The standard's uniform balanceOf and safeTransferFrom functions simplify bridge logic.

The standard is used in DeFi for representing fractionalized ownership and tokenized bonds or invoices. A single IERC1155 contract can issue multiple bond series (each with a unique ID) as fungible tokens, while also managing the unique legal documentation as a non-fungible token within the same contract. This creates a unified, auditable ledger for complex financial instruments.

Businesses adopt IERC1155 for supply chain and loyalty programs because one contract can track:

• Batch IDs of products (fungible tokens per batch).
• Unique serial numbers for high-value items (non-fungible tokens).
• Loyalty point tiers (different fungible token IDs for silver, gold, platinum). This reduces contract deployment overhead and provides a consolidated view of assets on a shared ledger.

Key features that make IERC1155 a preferred choice for developers:

• Batch Operations: Transfer multiple token types to multiple addresses in one call (safeBatchTransferFrom).
• Atomic Swaps: Swap any combination of tokens in a single transaction.
• Supply Tracking: Built-in functions to query total supply per token ID.
• Gas Efficiency: Significant savings over deploying separate ERC-20 and ERC-721 contracts for related asset ecosystems.

The standard is defined by a set of mandatory and optional interfaces. Critical functions include:

• balanceOf / balanceOfBatch: Check balances for one or many token IDs.
• safeTransferFrom / safeBatchTransferFrom: Transfer tokens.
• setApprovalForAll: Grant operator permissions for all tokens.
• supportsInterface: ERC-165 check for standard compliance. The optional ERC1155Metadata_URI extension provides a way to retrieve metadata for each token ID.

The safeBatchTransferFrom and safeBatchMint functions execute multiple transfers in a single call, creating a complex reentrancy surface. An attacker's contract receiving tokens via onERC1155Received could re-enter the batch operation before all internal state updates are complete.

• Critical: Ensure state updates (balances) occur before making external calls via _safeTransfer or _safeMint helpers.
• Defense: Use the Checks-Effects-Interactions pattern rigorously within batch logic.

IERC1155 uses setApprovalForAll(operator, approved) for approvals, granting the operator access to all of the caller's tokens of any ID. This is a broader scope than ERC-20's amount-specific or ERC-721's token-specific approvals.

• Risk: A malicious or compromised operator can drain all user assets.
• Mitigation: Implementers can consider supplemental mechanisms like ERC-1155 Permit (EIP-2612 style) for safer, single-use approvals. User education on the risk of setApprovalForAll is essential.

The safeTransferFrom functions mandate a call to onERC1155Received or onERC1155BatchReceived on the recipient if it is a contract. Improper validation can lead to locked or stolen assets.

• Must Revert: If the recipient contract does not return the correct magic value (bytes4(keccak256(...))), the transfer must revert.
• Gas Limits: Be aware of gas stipends for these calls; they are fixed and may fail for complex receiver logic, potentially blocking transfers to legitimate contracts.

Since a single contract manages fungible and non-fungible assets, internal accounting for balanceOf and totalSupply (if tracked) is critical.

• Integer Overflow/Underflow: Use Solidity 0.8+ or SafeMath libraries for all arithmetic, especially in batch operations where sums are calculated.
• Cross-Function Invariants: Ensure mint, burn, and transfer functions for one token ID cannot corrupt the balances or metadata of another token ID due to shared storage structures.

The uri(uint256 id) function returns a location for token metadata. A mutable or attacker-controlled URI is a central risk.

• Immutable Base URI: Consider setting a base URI in the constructor that cannot be changed, or using a decentralized storage solution like IPFS (ipfs://).
• Access Control: If the URI is updatable, protect the setter function (e.g., setURI) with strong access control (e.g., onlyOwner). A malicious update can change the perceived value and attributes of all tokens.

IERC1155 tokens are often deposited into lending protocols, marketplaces, or DAO treasuries. These integrations create composability risks.

• Balance Snapshots: Protocols that snapshot balances for rewards or voting must be aware that IERC1155 balances can change more frequently due to efficient batch transfers.
• Standard Compliance: Ensure your implementation strictly follows the EIP-1155 specification. Deviations (e.g., missing return values) will cause integrations to fail, potentially locking funds in other protocols.